In hospitals and so on, sterilization processing needs to be performed on objects to be sterilized such as a bandage for treatment, a scalpel, a pair of forceps, and a surgical gown that need to be sterilized. The steam sterilizers including a pressure vessel that stores the objects to be sterilized are often used to sterilize such objects to be sterilized as described above.
General steam sterilizers act to sterilize the object to be sterilized by introducing saturated water vapor into the pressure vessel to pressurize and heat it, and keeping a predetermined pressure and temperature for a certain time (refer to, e.g., patent literature 1).
The steam sterilizer described in Patent Literature 1 is the pressure vessel having a double-can structure including an inner can and an outer can forming a sterilization chamber that stores the object to be sterilized. A jacket portion is provided between the inner can and the outer can of the pressure vessel, and the saturated water vapor is introduced into the jacket portion. The inner can is heated with the saturated water vapor introduced into the jacket portion.
Further, the saturated water vapor is introduced also into an inner portion of the inner can. The inner can is pressurized and heated up to the predetermined pressure with the introduced saturated water vapor, and heated up to the predetermined temperature by the jacket portion around the inner can.
The inner can is kept at the predetermined pressure and the predetermined temperature with the saturated water vapor for the certain time, so that the sterilization is performed on the object to be sterilized stored in the inner can. After the certain time has elapsed, a gas-discharging process for discharging the saturated water vapor from the inner can is performed. In the inner can set in a vacuum state by the gas-discharging process, moisture adhering to the object to be sterilized is evaporated to dry it.
As described in Patent Literature 1, in the gas-discharging process, the saturated water vapor in the inner can is generally discharged by a vacuum pump.
Gas in the inner can is discharged by the vacuum pump not only when the gas-discharging process is performed, but also when a pre-warming process (conditioning process) is performed prior to performing the sterilization. In the pre-warming process, first, the inner can is brought into the vacuum state by the vacuum pump, the saturated water vapor is introduced from the jacket portion, and then a pressure of the inner portion of the inner can is raised to an atmosphere pressure with the saturated water vapor. The vacuum pump is driven to bring the inner can into the vacuum state again. This action is repeatedly performed a plurality of times to sufficiently pre-warm the object to be sterilized, and further replace air remaining inside the inner can with the water vapor, so that atmosphere in the inner can becomes closer to the saturated water vapor state.